Workout: Kirchhoff's principles
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Launch
the PhET simulation, Circuit Construction Kit - DC
Set up
Set up the circuit shown in the figure at the right by using 1 battery, 3 bulbs, 2 switches, and 11 wires. Turn on the voltmeter and check the box under "Tools" for "Non-Contact Ammeter". The voltmeter lets you read the potential difference between the tips of the two leads and the ammeter lets you read the current under the crosshairs.
Answer these questions
1. Leave both switches open so no current flows anywhere. The voltmeter is displaying the difference between the voltages measured on the two probes. Is it measuring the voltage on the black probe minus the voltage on the red? Or the other way around? How can you tell?
2. Now close the top switch. Where is there current found? What are the potentials at various points around the circuit. (Check along the wires as well as at the edges of the circuit elements.)
3. Now close both switches. How has the current changed in the circuit? How does the current in each of the bulbs compare to each other and to the current in the battery? Can you see how Kirchhoff's flow rule is working here?
4. In the situation in part 3, measure the voltage around the circuit, keeping the low end probe (the one subtracted) fixed at the low end of the battery. Is the voltage around the circuit what you expected? Why or why not?
Joe Redish, Spring 2017
Last Modified: May 2, 2019
